404 



BOTANY 



PART II 



further by budding; cell -fusions or union of nuclei frequently occur as a 

 preliminary (C, D). After the food-supply of the substratum is exhausted, the 

 conidia grow out into mycelial hyphae. Tlie formation of the conidia in the 

 damp manured soil of the grain fields is accomplished during a saprophytic mode 

 of existence, but the hyphal filaments which are eventually produced become 

 parasitic, and penetrate the young seedlings as far as the apical cone where the 

 inflorescence takes its origin. The mycelium continues its development in the 

 inflorescence, and ultimately terminates its existence by the production of brand- 

 spores. Xo conidia are formed on the host plant itself. 



In addition to the infection of young plants, either resting-spores or the conidia 

 resulting from their germination may be carried to the stigmas of the grass-flowers 

 and germinating there produce a mycelium which penetrates to the young seeds 

 and passes the winter in the embryo-plants. Such infection of the flowers maj- 



Fig. 3S7. —Tilletla Tritici. A, the basidium developed from the brand-spore bearing at the end 

 four pairs of spores fc (x 300); B, the dispersion of the spores wliioh have fused in pairs 

 (X 250); C, one of tlie paired spores germinating and bearing a sickle-shaped conidium ^-.7.- 

 (x 400). D, Mycelium with sickle-shaped conidia (x 350). (After Brefeld.) 



alone take place as in UsHIu{jo Tritici, U. Hordei, and U. antherarum, or the seed- 

 ling may more often be infected as in U. Avenue, U. Sorghi, U. Panici miliacei, 

 V. Crameri. The Smut of Maize can infect all parts of the plant while in a young 

 state and the disease is limited to tlie infected spots. 



The life-history of the Tilletiaceae is similar to that of the Ustilaginaceae. The 

 best-known species are Tilletia Tritici {=T. Caries) and TiUctia laevis, the fungi 

 of the stink-brand of wheat. The resting-spores fill the apparently healthy grains 

 and smell like decayed fish. In the first-named species the resting-spores are 

 reticulately thickened ; those of T. laevis, on the other hand, are smooth-walled. 

 Unlike the Ustilaginaceae, the germ-tube gives rise only at its apex to filiform 

 basidiosjiores, which are disposed in a whorl, and consist of four to twelve spores 

 (Fig. 337, A). Tlie basidiospores also exhibit tlie peculiarity that they coalesce 

 with one another in pairs in an H-form. Such cell fusions also occur between 

 germinating conidia of the Ustilagincae, but arc not accompanied by nuclear fusions. 

 Tlie filiform sjjores germinate readily, and produce sickle-shaped conidia at the apex 

 of the germ-tubes (Fig. 337, C). "When abundantly supplied with food material, the 

 germ-tubes grow into large mycelia, from which such sickle-shaped conidia are so 

 abundantly abstricted that they have the appearance of a growth of mould (D). 



